This invention relates to a slot array radiator, and more particularly, to a dual input/output port, dual polarization flat plate slot array antenna.
There long has been a need for an efficient, compact, flat antenna capable of generating coincident broadside beams with orthogonal polarizations, or a single beam whose polarization may be fully adjusted. It is well known that radar targets, for example, reflect different amounts of energy back to a radar receiver depending upon the polarization of the incident beam. The ability to readily change the polarizations from a single slotted planar array antenna greatly increases the capability of a radar detector. A radar detector employing the antenna of this invention is able to make the desired polarization change easily during target detection.
Slotted waveguide flat plate antennas are well known in the art. Such antennas also have been proposed for dual polarization and arbitrary polarization modes. In the past, the designs proposed have been handicapped by a number of design deficiencies. Previous to my invention, offered designs required the slots of such a flat plate array antenna to be positioned one waveguide wavelength apart. With such spacing, prior art antennas had low efficiencies for broadside beams because of the large gaps in the aperture, and so called "grating" lobes or "second order" beams resulted. The antenna disclosed hereinafter permits the slots to be placed one-half waveguide wavelength apart, thereby "filling" the aperture and eliminating grating lobes and obtaining higher aperture efficiency for broadside beams. In addition, as disclosed hereinafter, size of the antenna of this invention may be varied merely by altering the waveguide mode number, the numbers of rows and columns of slots, and adjusting the size of the top plate and the waveguide cavity. The prior art references of which I am aware include U.S. Pat. No. 3,599,216 ('216), which shows a circular polarized planar array antenna having alternately displaced transverse slots over virtual walls for one component, and a set of conventional shunt slots between virtual walls for the other component of a circularized polarized beam. The '216 patent, however, deals with a single port, single beam, fixed single circular polarization slotted waveguide broadside pencil beam antenna.
U.S. Pat. Nos. 3,623,112 and 4,063,248 and 4,353,072 all describe radiating elements which involve a combination of waveguide radiators and dipole radiators, the latter having coax and/or stripline feeding which limits RF power handling. Each functions in a manner substantially different from the invention disclosed hereinafter.
U.S. Pat. Nos. 2,982,960 and 3,281,851 and 3,348,227 and 3,503,073 show approaches that require full waveguide wavelength spacing between at least some of the radiating slots to achieve a broadside beam. That type of construction is a flaw if off-broadside second order beams are to be suppressed without using heavy and lossy dielectric loading in the waveguides.
U.S. Pat. Nos. 3,382,501 and 3,340,534 show a single port, single sense of circular polarization radiators formed by adding wire loops external to slots or open ended waveguides.
U.S. Pat. No. 4,197,541 shows a square coaxial transmission line radiator with coaxial line network elements which make the device unsuitable for use at millimeter wavelengths.
U.S. Pat. No. 4,266,228 shows ordinary cross slots on rectangular waveguides, which, as previously indicated, requires that the slot spacing be one waveguide wavelength apart in order to produce a broadside beam and would have second order beams under that condition.
The invention disclosed hereinafter provides a means to obtain two independent beams from a single slotted waveguide antenna. It does so with a compact "flat plate" design which is simple to manufacture. As will be appreciated by those skilled in the art, the fact that all of the slots are in a single slotted plate allows the use of precise photolithographic techniques, especially useful with millimeter wavelengths designs.
One of the objects of this invention is to provide a dual polarization slot antenna array with an independent terminal for each polarization.
Another object of this invention is to provide a dual polarization slot array antenna in which the slots of the radiating element may be positioned one-half waveguide wavelength apart, yet have the slots radiate in phase.
Another object of this invention is to provide a simplified antenna structure.
Another object of this invention is to provide an antenna structure which permit elliptical polarizations, linear polarizations, and circular polarizations from a single antenna structure.
Another object of this invention is to provide a single antenna structure which permits transmission on right circular polarization and receive on left circular polarization, or transmission on any desired polarization and receive on any different polarization.
Another object of this invention is to provide ease of fabrication for flat plate antennas regardless of how high a microwave frequency of operation is required.
Another object of this invention is to provide an antenna with lower resistive losses than obtained in flat plate antennas formed of a multiplicity of individual rectangular waveguides, each rectangular waveguide having slot radiators.
Another object of this invention is to allow the transmission of high microwave power levels without RF power breakdown, particularly for millimeter wavelengths.
Another object of this invention is to provide an antenna for passive "listen-only" systems for analysis of the polarization characteristics of received signals.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.